The objective of this proposal is to elucidate the molecular basis of steroid hormone regulation of gene expression. Ultimately, I wish to distinguish primary differentiation events at the DNA level from subsequent transcriptional modulation. These studies will employ two hormonally regulated systems (human growth hormone (hGH) and mouse sex-limited protein (Slp)) but will focus primarily on the second. Project 1 will continue definition of glucocorticoid responsive sites about the hGH gene, using gene transfer as an assay for regulatory features of DNA. This will identify questions that can be addressed using gene transfer, and will thus establish one approach to be used in the Slp study. Project 2 will contrast regulation of mouse S locus genes. Slp is controlled by androgens, while its homologous neighbor gene, Ss (encoding the fourth component of complement), is not under stringent hormonal control. Regulatory mutations exist in both genes, affecting levels of expression as well as Slp's dependence on androgen. Recombinant DNA technology will allow correlation of differences in DNA sequence with differences in expression of these genes. Mutant Slp genes that are constitutively expressed (i.e. androgen insensitive) will direct attention to regions of DNA necessary for hormone-receptor interaction. Other mutations will serve to define developmental regulation of Slp. Correlations of gene structure with gene function will further understanding of gene expression in general and steroid hormone action in particular.